In the past, a method of bonding a metal round rod to a metal rod has been known in which the body or stem portion of a metal round rod is inserted through a round hole formed in a metal plate and then is welded around the periphery of the stem portion to the peripheral edge of the round hole in the metal plate by electric welding technique. In another known method of bonding such metal members together, knurling is done on the neck portion of a metal round rod flanged at one end or the stem portion of the flanged rod immediately beneath the end flange and knurled stem portion is then pressed in to a round hole formed in a metal plate in a diameter slighlty smaller than that of the stem portion so as to be bonded or rigidly secured to the metal plate.
Difficulties, however, have been experienced in these previous bonding methods on account of various technical problems involved therein. In the first method, which utilizes welding, occurrence of more or less thermal stress and strain is unavoidable and this necessitates special external surface treatments on the assembly produced for correction in angle between the metal plate and the metal round rod bonded thereto and for removal of defects resulting from head seizure, thus causing an increase in the cost of production. In the second method, which employs a knurling operation, the adhesion or bond strength obtainable between the metal round rod and the metal plate is unstable and limited particularly for forces that act on the metal rod in the direction from its distal end to the flange end, that is, in the direction opposite to that in which the metal round rod has been driven into the metal plate. In order to overcome this situation, it is required that the metal round rod be made of a high-quality special alloy steel (usually containing at least one of rare, alloying elements such as nickel, chromium, molybdenum, vanadium, and manganese) and be subjected to a particular heat treatment, thus involving a substantial increase in expense. Even with such measures resorted to, however, the adhesion or bond strength between the metal members must still be unstable since there is no guaranteeing of any mechanical bonding between the metal member that is effective under impact forces acting upon the metal rod in the direction from its free end toward its flanged end.
Under the circumstances, the present invention is intended to solve such previously encountered problems.